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Is spray foam insulation the right solution for your renovation project? We explore the manufacturers’ claims, the evidence and the risks.

What is it?

Spray-Foam Insulation is a rigid foam that is lightweight, and can be sprayed onto the underside of a roof at a thickness of approximately 50 to 100mm. This type of insulation foam is made up of polyurethane and is sprayed into place as a liquid. On contact, the foam slowly expands to up to 100 times in size to create an effective insulating layer of hardened foam.

Claims made by the Manufacturers:

The manufacturers claim that the spray foam expands completely, filling all cavities and voids. It eliminates air leakage in your roof, and is an effective sound barrier. The system is the most suitable form of insulation for roof, attic or loft space, as well as floors and walls, in both new and existing properties.

Allergies and some forms of asthma are often caused by airborne particles such as dust, dirt, car fumes, garden fire smoke, etc. It is claimed that spray foam insulation protects property from a wide range of such pollutants.

It will help to deter pests, as they will find it much harder to find a way in.

Furthermore, the spray foam stops tiles and slates from slipping and strengthens the roof by holding them in place. The foam will also protect water tanks and pipes from freezing.

Sounds perfect. However, let’s look at the evidence to date:

The main argument against spray foam has been that any dampness getting in, or condensation being caused, leads to rotting of roof trusses and battens. Some experts say that it is timber’s number one enemy. Once present, the condensation has nowhere to go but into the timber and, in due course, will cause rot.

The rain from the outside can get in through a tile or slate that has become displaced, (this has happened, even though the foam is claimed to prevent tile and slate movement).

There have been numerous reports from homeowners, complaining that they have not been able to repair their roof when it is leaking, due to the presence of this foam.

The manufacturers insist that ‘the system is the most suitable form of insulation for roof, attic or loft space in both new and existing properties’. However, older properties, for instance, have a different construction to modern builds, both in material used and their design, and there is still no evidence to suggest that spray foam insulation is a cure-all for every property.

Indeed, many independent surveyors still do not like it or recommend it and many who are valuers will down-value a property if this type of insulation has been installed.